The long-term goal of the proposed research is to describe the signal transduction pathway that leads to bacterial chemotaxis in chemical terms. The bacterial chemotaxis signaling system has emerged as an archetype for transmembrane signaling and molecular information processing. Investigations of this system have revealed that signals are transmitted through a macromolecular assembly of the chemoreceptors and their associated signaling proteins. A forefront research objective is to understand the molecular mechanisms that underlie the ability of this higher order protein assembly to transmit signals. The three Specific Aims of this application follow. Aim 1 is to use synthetic ligands, protein engineering, and nanoparticles in conjunction with electron cryotomography to determine the organization of the signaling array and how chemoeffectors influence it. Aim 2 is to implement chemical biology strategies compatible with native membrane preparations to elucidate protein-protein interaction surfaces in the reconstituted signaling lattice. Aim 3 is to probe the relationship between the microbial responses of chemotaxis and swarming using tools developed in Aims 1 and 2. In pursuing these Aims, we shall employ methods and ideas from organic chemistry, microbiology, protein engineering, polymer and materials chemistry, structural biology, and chemical biology. We anticipate that this research will provide insight into the molecular mechanisms that underlie chemotactic signaling and swarming in bacteria as well as new tools and strategies to explore signal transduction pathways in general.